Hot deformation behavior and deformation mechanism of γʹ strengthened Co-based superalloys

Abstract

Hot tensile experiments were carried out using LE 5105 electronic universal testing machine to study the hot deformation behavior at temperatures of 900–990 °C and strain rates of 0.0001–0.0125s⁻¹. The results show that the peak flow stress decreases with increasing temperature and decreasing strain rate, and the flow curve of Co-7Al-7W superalloy belongs to the typical dynamic recrystallisation (DRX) type. The flow instability regions are 900 °C/0.0005s⁻¹ and 930–960 °C/0.0025–0.0125s⁻¹, the flow stability regions are 900 °C/0.0025s⁻¹-0.0125s⁻¹、960°C–990 °C/0.0001s⁻¹-0.0005s⁻¹. The instability regions is mainly composed of deformed grains, and as the temperature increases, most of the grains in the stable region are fine equiaxed recrystallized grain structures. The microstructure analysis of the Co-7Al-7W superalloy using EBSD reveals that the DRX nucleation mechanism of the Co-7Al-7W alloy is predominantly DDRX, with CDRX playing only an auxiliary role in nucleation. The presence of γʹ phase inhibits dislocation migration, delays DRX, and hinders nucleation and growth of recrystallized grains.